1. Field of the Invention
The present invention relates to a zoom lens optical system suitable for cameras that use solid state imaging devices, and more particularly, to a zoom lens optical system which is compact, has a high zooming ratio and telecentricity, and corrects a color aberration.
2. Description of the Related Art
The spread of electronic still cameras and video cameras using a solid state imaging device, such as, a charged coupled device (CCD), a complementary metal oxide semiconductor (CMOS), or the like, are rapidly extending of late. Such cameras are being developed to become cheaper, lighter, and more compact. Accordingly, a zoom lens optical system used in these cameras is also required to be less expensive, lighter, and more compact.
A camera using such a solid state imaging device employs a crystal filter to prevent the Moire phenomenon caused by a periodic structure of the solid state imaging device. Hence, a sufficiently great back focal length should be ensured in consideration of a thickness and a location of the crystal filter, and telecentricity of a ray incident upon an image plane is an important factor.
In this regard, Japanese Patent Publication No. 2003-098433 discloses a 4-group zoom lens optical system. The 4-group zoom lens optical system includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power, which performs both aberration compensation and focusing, which are sequentially arranged from an object. The second and third lens groups perform zooming.
The 4-group zoom lens optical system comparatively satisfies a great back focal length and the telecentricity. However, the 4-group zoom lens has difficulty in producing a high-resolution image, because a large amount of aberration remains. Moreover, the 4-group zoom lens has only a zooming ratio of about 3, which does not achieve a high zoom ratio.
Japanese Patent Publication No. 2002-156581 discloses a 5-group zoom lens optical system. The 5-group zoom lens optical system includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power, and a fifth lens group having a positive refractive power, which are sequentially arranged from an object. The 5-group zoom lens optical system performs zooming by moving the second and fourth lens groups. During this zooming, the first and third lens groups are fixed. Thus, an overall length and a size of the 5-group zoom optical system should be increased to correct optical performance when the optical system is at a wide angle position.